On Tue, 2015-05-05 at 15:00 +0200, Thomas Gleixner wrote: > On Sat, 25 Apr 2015, Eric Dumazet wrote: > > On Thu, 2015-04-23 at 14:45 +0200, Thomas Gleixner wrote: > > > > > You definitely have a point from the high throughput networking > > > perspective. > > > > > > Though in a power optimizing scenario with minimal network traffic > > > this might be the wrong decision. We have to gather data from the > > > power maniacs whether this matters or not. The FULL_NO_HZ camp might > > > be pretty unhappy about the above. > > > > Sure, I understand. > > > > > > To make this clear, here the profile on a moderately loaded TCP server, > > pushing ~20Gbits of data. Most of TCP output is ACK clock driven (thus > > from softirq context). > > > > (using regular sendmsg() system calls, that why the > > get_nohz_timer_target() is 'only' second in the profile, but add the > > find_next_bit() to it and this is very close being at first position) > > > > > > > > PerfTop: 4712 irqs/sec kernel:96.7% exact: 0.0% [4000Hz cycles], > > (all, 72 CPUs) > > ----------------------------------------------------------------------------------------- > > 10.16% [kernel] [k] copy_user_enhanced_fast_string > > 5.66% [kernel] [k] get_nohz_timer_target > > 5.59% [kernel] [k] _raw_spin_lock > > 2.53% [kernel] [k] __netif_receive_skb_core > > 2.27% [kernel] [k] find_next_bit > > 1.90% [kernel] [k] tcp_ack > > > > Maybe a reasonable heuristic would be to > > change /proc/sys/kernel/timer_migration default to 0 on hosts with more > > than 32 cpus. > > > > profile with timer_migration = 0 > > > > PerfTop: 3656 irqs/sec kernel:94.3% exact: 0.0% [4000Hz cycles], > > (all, 72 CPUs) > > ----------------------------------------------------------------------------------------- > > 13.95% [kernel] [k] copy_user_enhanced_fast_string > > 4.65% [kernel] [k] _raw_spin_lock > > 2.57% [kernel] [k] __netif_receive_skb_core > > 2.33% [kernel] [k] tcp_ack > > Is that with the static key patch applied?
This was without. I applied your patch on current linus tree, but for some reason my 72 cpu host is not liking the resulting kernel. I had to ask for a repair, and this might take a while. Note your kernel works correctly on other hosts, but with 48 or 32 cpus, so this must be something unrelated. I'll let you know when I get more interesting data. Thanks -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
